1. Field of the Invention
This invention relates to an application specific integrated circuit (ASIC) and, more particularly, to an ASIC having a redundancy capability for replacement of defective embedded memory subunits of a memory instance in the ASIC.
2. Prior Art
In the design and production of an ASIC, a compiler, or higher level computer program, is used by an ASIC designer to convert the designer's keystroke inputs from a workstation to tape-out information that is used for generating production masks that are used to fabricate an ASIC chip. An ASIC design can have a number of different functional units provided on a single chip. These functional units include one or more embedded memory instances, or blocks, such as, for example, embedded random access memory (RAM) blocks, that are physically co-located in close proximity to various other types functional blocks on the ASIC.
Sometimes, an embedded memory instance has a defective memory subunit, such as a defective row or a defective input-output (I/O) unit. An I/O unit is a group of several memory columns and a multiplexer that is used to select a particular one of the memory columns for I/O operation. After an ASIC is fabricated and tested, various defective bits (if any) in the memory instances in a particular subunit need to be corrected or replaced by redundant memory circuits. One redundancy technique uses a fuse array that is provided by the compiler to store an address of a defective subunit of an embedded memory instance.
Prior art memory redundancy techniques are focused on stand-alone memories. A stand alone memory chip uses a very limited number of functional units in its design while an ASIC uses a considerably larger number of different functional units in its design. In an ASIC, co-locating a fuse array in the vicinity of a memory instance complicates the design and operation of the ASIC. For example, fuse arrays take up large amounts of chip area and the structure and fabrication of such a fuse array may not be compatible with the structure and fabrication of an ASIC embedded memory instance or other functional blocks located near an embedded memory instance in an ASIC. Consequently, there is a need to provide an improved redundancy architecture for embedded memories in an ASIC chip.